Self-Diffusion Coefficients for Pure and Mixed Adsorbate Fluids in Narrow Pores

The equilibrium distribution and the concentration dependence of the local and average self-diffusion coefficients for pure fluid and binary mixture components in narrow slitlike pores were analyzed. The coefficients were calculated using the lattice gas model in the quasi-chemical approximation on the assumption of a spherical shape and approximately equal sizes of the components. For the pure adsorbate, these calculations were compared with molecular dynamics simulations. Both methods gave similar concentration profile changes and dynamic characteristics of interlayer particle redistributions in strong nonuniform adsorption fields for dense fluids. A satisfactory agreement was obtained for the temperature dependences of the self-diffusion coefficients along the pore axis. The influence of the molecule–wall potential and of intermolecular interaction were considered. The self-diffusion coefficients of the adsorbate were shown to strongly depend on the density of the mixture and the distance from pore walls.